The present invention relates to a dry etching method by which various materials are etched by etchant plasma for manufacturing a semiconductor device, and to a device used for the dry etching method.
Semiconductor integrated circuits are processed with elaborate circuit patterns. This tendency has recently increased. For example, an VLSI having a minimum pattern of 1 to 2 .mu.m has been developed. In order to accomplish pattern dimension described above, dry etching using an etchant plasma is inevitably the etching method. In the dry etching process, an etchant, that is, a reactive gas, is introduced into a reaction chamber which has parallel plate electrodes. Power, for example, high frequency power or direct current power, is applied across the electrodes to generate a plasma with glow discharge. Positive ions within the plasma are accelerated by a cathode fall voltage in the direction of the cathode, and bombard a sample placed on the cathode thereby etching it. This dry etching process is also called reactive ion etching.
However, according to this conventional dry etching, the etching rate is very low and the etching takes long time. For example, the etching rate of SiO.sub.2 is about 300 .ANG./min when a gas mixture of CF.sub.4 and H.sub.2 is used as the etchant, so that it takes about 40 minutes to etch a SiO.sub.2 film which has a thicknenss of 1 .mu.m. The etching rate of phosphorus-doped polycrystalline silicon is about 500 .ANG./min when a CBrF.sub.3 gas is used as the etchant, so that it takes about 8 minutes to etch a phosphorus-doped polycrystalline silicon film which has a thickness of 4,000 .ANG.. Further, the etching rate of aluminum is about 1,000 .ANG./min when a CCl.sub.4 gas is used as the etchant, so that it takes several ten minutes to etch the aluminum film which has a thickness of 1 .mu.m. This low etching rate essentially results from low ionizing efficiency, for example, in the range of 3 to 5% in the glow discharge between the parallel plate electrodes.
In order to increase the etching rate, the high frequency power, for example, may be increased so that the etching rate is slightly increased. However, increasing the high frequency power has drawbacks in that a great amount of the high frequency power is converted to heat, degradation of a photoresist film to be used as the etching mask occurs in accordance with an increase of the cathode fall voltage or the like, and a silicon substrate may electrically damaged. In consideration of these drawbacks, the increase in the etching rate is generally sacrificed so that the high frequency power is usually applied as low as possible. Recently, it has been reported that high-rate etching of Si and Al.sub.2 O.sub.3 has been accomplished using a three-electrode power supply device with a means which supplies electrons within the plasma itself (J. Vac. Sci. Technol, 17(3), 731, by N. Heiman et al, 1980). However, in this case, a heating filament is used so that the filament is corroded by the reactive gas. This method may have a problem in continuous application for a long period of time. In order to increase the density of the etching source, a method for using a laser has been proposed (J. Electrochem. Soc. 127, 514, by J. I. Steinfeld et al, 1980). According to this method, the density of the etching source increases, and a high etching rate is accomplished. However, the etching source which has increased mainly consists of neutral radicals. Since the neutral radicals are not attracted by the cathode, directivity of the movement is uncertain. Side etching may occur, so that neutral radicals are not used for elaborate patterning of less than 1 .mu.m.